Electric measuring instrument.



Patented Dec. I6, 1902.

2 Sheats-Sheet l.

In VTI COT": RoberC H. Read n H READ ELECTRIC MEASURING INSTRUMENT.(Application filed May 20, 1901-) Witnesses:

I No. 716,!03. Patented Dec. l6, I902.

1 R, H. READ.

ELEGTBlC MEASURING INSTRUMENT. (Application filed May 20, 1901.) V (inModel.) 2 Shaets$heet 2.

Inventor:-

I Wifineses:

Rbberfi H Read ROBERT H. READ, OF SCHENECTADY,

MATENT FFICE.

:NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF: NEWYORK.

ELECTRIC M EASURING INSTRUMENT.

SPECIFICATION formingpart of Letters Patent No. 716,103, dated December16, 1902.

Application filed May 20, 1901.

To all whom it may concern.-

Be it known that I, ROBERT H. READ, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Electrical MeasuringInstruments, (Case No. 1,671,) of which the following is aspecification.

This invention relates to electrical measurro ing instruments, theobject being to provide an instrument for measuring electric currentscheap in construction, accurate in its indications, and not liable toget out of order, and one in which the moving parts have a minimumamount of inertia.

It is a familiar scientific principle that a conductor stationed in" amagnetic field. if traversed by a current developing a field of forcearound the conductor at an angle to the line of flux of the magneticfield will have a tendency to move in the field. I utilize thisprinciple in the construction of an electrical measuring instrument bymounting a spiral conductor, which may be in the form of a thin wire orribbon one end of which is fixed to a stationary part of the instrumentand the other to an arbor carrying an index-needle. The spiral conductoris placed in a dense magnetic field produced either by a permanent orelectro magnet, and when traversed. by a current the magnetic field inwhich it is located reacts upon the field of force around the conductorand the spiral dilates or contracts, according to the direction of thecurrent, and produces a rotary effort on the arbor or pivot-post, whichgives a deflection to the needle. In order to increase the rotaryefiect, two or more spiral conductors may be employed and a current maybe led through them in parallel or in series relation, the field offoroein which they are placed being so arranged with respect to ,thedirection of current circulating in the spirals that a summative torqueis produced on the needle. When arranged in series, the current may becarried inwardly toward the pivot-post on one spiral and outwardly fromthe same on the other and the several spirals be placed in independentfields in which the direction of flux is re- 50 versed. The independentfields may be afforded by a system of consequent poles prothe spiral andthe electromagnetic forces, the

ment, to a maximum deflection of ninety de- Serial No. 60,991. (Nomodel.)

duced in a permanent or electro magnet. Where the several spiralsareconnected in parallel, the current may be led'through them inparallel to the pivot-post and carried from the same by a spiral springor conductor. With the series arrangement of the spiral conductors thetwo spirals being secured to the arbor in opposite directions preventderangement of accuracy in the instrument by reason of any change oftemperature in the spirals, since any tendency of one coil to lengthenunder rise of temperature will be compensated by a tendency in theopposite direcelectromagnetic effects aflecting indications Ion theinstrument the efiorts are summative. One great advantage afforded in aninstrument of this type is the small inertia of the moving parts. Thepointer may be made exceedingly light, and practically the only inertiais due to the pivot, which is the only massive part of the movingsystem, and as its weight lies close to the mathematical axis ofrevolution the inertia is very small. Another advantage of theorganization is that the range of the instrument may be made as wide asdesired, since the angle of deflection depends upon the length andcross-section of effort of the spirals to wind or unwind beingcontinuous until the impelling force balances the retracting force. Therange is not, therefore, limited, as in the ordinary type of instrurees.D My invention comprises a current-carrying conductor mounted in amagnetic fiield having one end fixed to a stationary part of theapparatus and the other end connected to the index or pointer.

More specifically considered, it comprises a current carrying spiralmounted in a magnetic field and arranged to give a deflection by achange of shape of the spiral under change 5 of currents.

It comprises also other features, the novelty of which will behereinafter more fully described, and definitely indicated in the claimsappended to this specification.

In the accompanying drawings, which illustrate my invention, Figure 1 isaperspective View of an ammeter embodying my improvel ments in whichcurrent is passed in series through two spiral conductors both securedto the rotary arbor carrying the index-needle. Fig. 2 is a centrallongitudinal section of this form of the instrument. Fig.3 is a detailshowing the arrangement of the spiral conductors and the index-arbor.Fig. 4 is a side elevation of another type of the instrument in to whichcurrent is carried in parallel through two spiral conductors. Fig. 5 isan end view of this type, and Fig. 6 is a detail showing the arrangementof the spiral conductors and needle-arbor. 7

Referring first to the type shown in Figs. 1, 2, and 3, 1 represents anelectromagnet having three legs, so as to develop a consequent polebetween two opposite poles having the same sign. The magnet might alsobe formed from two permanent magnets having two similar poles placed incontact. The poles of the magnet are bored with a small hole toaccommodate an arbor 2, mounted in jewel-bearings at the top and bottomcarried in adjusting-screws 3 4. Between the two pairs of poles NS SN isformed a narrow gap in which are placed spiral conductors 5 6, havingtheir outer ends fastened in fixed supports 7 8, mounted oninsulating-supports around the jewel-posts and rotative therein when theposts are loosened to adjust the zero of the instrument. The inner endsof the spiral conductors are fixed to the arbor 2. The spiral conductorsare mounted so that current in entering from the post 7 will flow aroundthe arbor in the same direction through both spirals-that is to say, ithas an anti-clockwise rotation in the conductor 6. It has a similarrotation in the conductor 5. -With such an organization, the conductors5 and 6 being in reverse fields, since the lines of force flowdownwardly between the upper and middle pole-pieces and upwardly throughthe lower and middle pole pieces, if the tendency of the spiral 6 is toopen or dilate that of the spiral 5 will be to close or contract, and byreason of the outer ends of the spiral being fixed these twotend enciesadd together in rotating the index-arbor. With respect to the expansionof the springs under heat, however, the efforts of the two springsbalance one another and the zero of the instrument is undisturbed. Aninstrument of this type gives nearly a pro- 5 5 portional scale, whilethe range of the scale may be Varied by change of length or stifiness ofthe spiral conductor. The large radiating-surface afforded by theribbonconductors permits them to rapidly take the temperature due to anycurrent passing. The

resistance of the instrument is very low, and the index comes quickly torest at the deflection corresponding to the current being measured.Where light currents are employed, the instrument should be supported ina vertical position to prevent tendency to sag of theconducting-spirals, a tendency which would produce frictional contactwith the pole-faces and introduce a source of error. To prevent damageto the instrument from accidental contact from jarring or other causes,the pole-faces may be covered with a thin layer of mica or otherinsulation. The spiral conductors may be placed in parallel with ashunt, as common in many types of ammeters, and the electromagnetsexcited by a separate or by the same source.

In thetype of instrument shown in Figs. 4,

5, and 6 two permanent magnets are juxtaposed so as to form a compoundmagnet, on the poles of which are mounted annular iron pole-pieces 9 10,between which is supported on brass brackets an intermediate disk ofiron 11. The spiral conductors are fixed in parallel relation to a post12, the inner ends being fastened to the arbor, and current is ledtherefrom through a spiral retractingspring 13. In this type ofinstrument the direction of the magnetic flux in the two fields is thesame. The current is led to the two spirals in parallel with a commonsupport 12 and passes out through the arbor and retracting-spring 13. Inthe type of instrument shown in Figs. 1, 2, and 3 the fields werereversed and current flowed through the two spirals in the samedirection. In this case the current flows through the two spirals inreverse direction by reason of the multiplearc relation, and the torqueis therefore sum mative. In this instrument the winding effort on thespirals has two components, one due to attraction of parallel currentsand the other due to the shifting of the current-carrying conductor inthe magnetic field. In the case of the unwinding-spring this efiort is adifferential of the two components, the electrom agnetic effort being inexcess. The force of the component due to attraction of paral lelcurrents may be variedby changing the pitch of the spirals.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. An electric measuring instrument havinga current-carrying conductormounted for lateral movement in a narrow gap between the poles of amagnet, said conductor being fixed at one end and connected at the otherwith an indicating device.

2. An electric measuring instrument having an elastic current-measuringconductor mounted in a narrow gap between the poles of a magnet, bothends of said conductor having a solid connection with the leads of thecircuit, and an indicator operated by movement of the conductor in thefield.

3. An electric measuring instrument comprising a spiralcurrent-measuring conductor crossing a narrow gap between twomagnetpoles, having one end fixed and the other connected to anindicator.

4. An electric measuring instrument comprising a spiral electricconductor mounted in a narrow gap between two magnet-poles havingitsinnerend connected to an indicator and its outer end secured to a fixedpoint.

, 5. An electric measuring instrument comprising a spiral conductormounted between the poles of a magnet, a pivoted indicator secured toits inner or central end and a fixed point of attachmentat the outerend.

6. A currentemeasuring instrument comprising a spiral current-carryingconductor mounted between the poles of a magnet, an arbor secured to itsinner or central end extending through the poles of the magnet, apointer secured to thearbor outside the poles of the magnet and a fixedpoint of attachment for the outer end of the spiral.

7. An electric measuring instrument comprising a spiral metal ribbonmounted in a magnetic field, having its inner or central end fieldsinclosin g the said conductors, the directions of flux of the severalfields with respect to the direction of current being such as to providea summative torque.

In Witness whereof I have hereunto set my hand this 17th day of May,1901.

ROBERT H. READ. Witnesses:

BENJAMIN B. HULL, FRED Russ.

